PROCESS FOR CONVERTING ACETALS TO ETHERS

Abstract: The present invention relates to a process for converting acetals to ethers. More particularly, this invention relates to a hydrogenation process for converting a 3-alkoxypropionaldehyde dialkyl acetal to the corresponding 1,3-dialkoxypropane in the presence of a supported hydrogenation catalyst. The process is highly selective towards the formation of the foregoing diethers relative to the formation of the corresponding alcohols, alkoxylated alcohols and mono-ethers.

Description: PROCESS FOR CONVERTING ACETALS TO ETHERS This application is a continuation-in-part of U.S. Application Serial No. 08/087,977, filed July 7, 1993. The disclosure in this application is incorporated herein by reference in its entirety. Technical Field The present invention relates to a process for converting acetals to ethers. More particularly, this invention relates to a hydrogenation process for converting a 3-alkoxypropionaldehyde dialkyl acetal to the corresponding 1,3-dialkoxypropane in the presence of a supported hydrogenation catalyst. The process is highly selective towards the formation of the foregoing diethers relative to the formation of the corresponding alcohols, alkoxylated alcohols and mono-ethers. Background of the Invention It is reported in "Acrolein", C W Smith, Editor, John Wiley & Sons (1962) at page 114 that the diethyl acetal of ethoxypropionaldehyde undergoes hydrogenolysis in the presence of Raney nickel to form the diethyl ether of 1,3-propanediol. The following equation is given: C2H 5 OCH2CH 2 CH(0C2H5)2 — ■> C2H5OCH2CH2CH2OC2H5 + C 2 H 5 OH US Patent 2,425,042 discloses tjie catalyzed reaction (R 1 θ) 2 C(R)CH(OR 1 ) 2 + 2H 2 → R 1 OCH(R)CH 2 OR 1 + 2R 1 OH wherein R is hydrogen or methyl and R^ is an alkyl, aralkyl, alkoxyalkyl, alkoxyalkenyloxyalkyl or alkoxy-polyalkenyloxy-alkyl radical. The reference indicates that the preferred catalyst is Raney nickel, although other hydrogenation catalysts such as copper- chromium oxide, platinum and palladium black can be used. US Patent 2,590598 discloses the catalytic hydrogenation reaction R"CH(OR' ) (CH 2 CH(OR) ] n CH 2 CH(OR) 2 → R"CH(OR' ) [CH 2 CH(OR) ] n CH 2 CH 2 OR + ROH wherein each R represents the same or different hydrocarbon radicals chosen from the group consisting of alkyl, aryl and aralkyl radicals, and n is a whole number including 0 and generally less than 10. The reference indicates that Raney nickel is the preferred catalyst but "other metal hydrogenation catalyts (ie, platinum or palladium) or copper, chromium etc." can be used. A particular aspect of this disclosure is that there is no disclosure of the hydrogenation of a propane ether nor the use of a supported catalyst. US Patent 4,479,017 discloses the catalyzed hydrogenation reaction [R(YO) n ] 2 C(R 1 )(R 2 ) → RfYOJnCHfRiM ) wherein R represents a hydrogen atom or a lower alkoxy group, Y represents an alkylene group having 2 to 12 carbon atoms, n is a positive number of 1 to 6, the two groups R(YO) n may, together with the carbon atom to which they are bonded, represent a 1,3-dioxolane ring, and R 1 and R 2 , independently from each other, represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of R 1 and R 2 represents a hydrogen atom. The catalyst is a "palladium catalyst supported on a carbon carrier in the absence of an acidic substance added". This reference does not disclose the hydrogenation of triethers. Therefore, it cannot be predicted as to what might be the effect of a third ether group in the molecule being hydrogenated. Moreover, this reference states that, for their hydrogenation reaction, a palladium on carbon catalyst when used in the absence of acid co-catalyst is superior to the same catalyst when used in the presence of an acid co-catalyst. Furthermore, this reference states that, for their hydrogenation reaction, a palladium-on-alumina catalyst in the absence of an acid substance added cannot achieve the excellent improvement shown by palladium on carbon catalyst of that invention. Summary of the Invention This invention is directed to a process for making a 1,3- diether compound represented by the formula: RO.CH 2 .CH 2 .CH 2 .OR (I) wherein R is an alkyl group having 1 to 4 carbon atoms, the process comprising hydrogenating an acetal of the formula RO.CH 2 .CH 2 .CH(OR) 2 (II) wherein R has the same meaning as in formula (I) above, in the presence of a catalyst composition comprising at least one catalytic metal selected from the group consisting of Pd, Ni, Co, Pt, Rh and Ru and a support material, said support material being one or more selected from the group consisting of silica, alumina, silica- alumina, aluminosilicates and carbon. Description of the Preferred Invention The acetal reactant hydrogenated has the formula (II) and R in this formula preferably represents an ethyl group. Such compounds are known in the art. For instance, a compound of formula (II) can be produced by reacting an unsaturated aldehyde, eg acrolein, with an alcohol, R.OH, with at least one acidic reagent for an effective period of time to form the desired acetal. The molar ratio of the aldehyde to alcohol is preferably about 1:1 to 1:20, more preferably about 1:3 to about 1:10. In one embodiment, water is also present in the feed to the reaction. The concentration of water in the feed can be up to about 35% w/w based on the combined weight of aldehyde and alcohol in the reaction mixture and is preferably from about 1% w/w to about 10% w/w, eg about 5% w/w. The acidic reagent can be a solid. Examples of such solid acidic reagents include Amberlyst®15 and Amberlyst*35, both of which are available from Rohm & Haas and are strongly acidic cationic macroreticular sulphonated polyvinyl styrenes. Other acidic reagents that may be used include one or more of mineral acids such as hydrochloric acid, sulphuric acid, sulphonic acid or phosphoric acid; one or more C1-C7 (i) mono- or dicarboxylic acids or (ii) halogenated fatty acids; alkyl and aryl sulphonic acids such as eg methane sulphonic acid and para-toluene sulphonic acid; and ammonium and a ine salts of any of the foregoing mineral or organic acids. The reaction to produce the acetal from the unsaturated aldehyde can be conducted in a batch, continuous or semi-continuous mode in a fixed bed or a slurry reactor. The reaction to produce the acetal is preferably conducted at a temperature in the range of about 0°C to about 120°C, more preferably from about 20°C to about 80°C. The reaction pressure is preferably in the range of about 0 kPa to about 700 kPa, more preferably from about 0 kPa to about 150 kPa. The average residence time of the aldehyde with the acidic reagent is preferably from about 5 minutes to about 20 hours, more preferably from about 15 minutes to about 10 hours. This reaction produces a mixture of products principally containing the unreacted aldehyde and alcohol, the corresponding alkoxyaldehyde and the unsaturated acetal, the desired acetal and water. The desired acetal is separated and the other organic components and some of the water can be recycled to the reactor where the acetal is formed. The acetal is converted to the diether by catalytic hydrogenation. The hydrogenation reaction is suitably carried out at hydrogen pressures of about 650 kPa to about 35,000 kPa, preferably from about 1,500 kPa to about 20,000 kPa, more preferably from about 3,000 kPa to about 17,500 kPa eg from about 4,500 kPa to about 7,500 kPa. The mole ratio of the acetal (II) to hydrogen can be from about 1:1 to about 1:100, and is preferably from about 1:2 to about 1:50. The hydrogenation catalyst composition comprises at least one catalytic metal selected from the group consisting of Pd, Ni, Co, Pt, Rh and Ru on a support material. Pd and Ni are the preferred metals and Pd is especially preferred. The support material for the catalytic metal is one or more selected from the group consisting of silica, alumina, silica-alumina, aluminosilicates and carbon. The carbon, where used, can be one of the many forms of carbon eg graphite or activated carbon. The catalytic metal may be deposited or impregnated on the support using conventional mixing or precipitation techniques. The catalyst composition suitably has a catalytic metal content of about 0.05% w/w to about 80% w/w. Within this range, when a relatively less active metal such as eg nickel is used as the catalytic metal, it is suitably used towards the higher end of this range, whereas when a relatively more active metal such as palladium is used as the catalytic metal, it is preferably used at the lower end of this range. Thus, for instance, the preferred range for the less active catalytic metals is suitably from about 20% w/w to about 80% w/w, whereas for the more active catalytic metals the preferred range is suitably from about 0.05% w/w to about 20% w/w. The weight ranges quoted above are based solely on the weight of the catalytic metal and the support and does not take into account any water or moisture content associated with either component. Examples of commercially available catalysts that are useful include inter alia (i) Escat®10 (ex Engelhard Industries) which contains 5% w/w of palladium on activated carbon powder and has a surface area of 850 m 2 /g and a moisture content of about 52.5% w/w; (ii) Escat®14 (ex Engelhard Industries) which contains 5% w/w of palladium on activated alumina powder having a surface area of about 125 m 2 /g; and (iii) Ni-3266E (ex Engelhard Industries) which contains a calcium promoted silica/alumina supported metal catalyst having a nickel content of about 50% w/w and a surface area of about 150m 2 /g, and is in the form of 1/16-inch extrudateε. The reaction may optionally be carried out in the presence of a solvent. Examples of such solvents include inter alia alcohols, ethers and esters. Polar solvents such as alcohols are preferred although in this case the alcohol used should be such that the oxyalkyl group of the alcohol solvent corresponds to the oxyalkyl group in the desired 1,3-diethyl ether (I). A sufficient amount of solvent can be used to dilute the acetal reactant (II) to the desired concentration to facilitate handling and/or to maintain the reaction mass in solution. The hydrogenation reaction is suitably carried out at a temperature in the range from about 50°C to about 250°C, preferably from about 100°C to about 225°C and more preferably from about 125°C to about 225°C, eg from about 150°C to about 210°C. The hydrogenation of the acetal with hydrogen in the presence of a catalyst composition as described above can be carried out in a slurry reactor, a fixed bed reactor, a spouted bed reactor or any other suitable reactor configuration such as eg a moving bed reactor. The reactants may be in a gaseous phase and/or a liquid phase. The reaction can be carried out in a continuous, semi-continuous or a batch-type mode. The average residence time of the acetal reactant (II) in contact with the catalyst composition during the formation of the corresponding 1,3-diether compound (I) is suitably from about 5 minutes to abaout 30 hours, preferably from about 15 minutes to about 10 hours. In the various embodiments of the process of the present invention to produce the 1,3-diether compound of formula (I), one or more of the following compounds may be generated as by-products: a) R.OH b) 3-alkoxy propanol-1 c) 1-propanol and d) alkyl propyl ether Of these, (a) is always a generated as a product during the hydrogenation of the acetal. However, the present process has the significant advantage that it is particularly selective towards the formation of the desired 1,3-diether (I) relative to the formation of the by-products (b)-(d) above. Thus, in one embodiment, the selectivity of the inventive process towards the formation of (I) relative to the formation of the combined amounts of (b)-(d) is at least about 60 mole % and is preferably at least about 90 mole %. Whilst it is preferable for the process to be carried out in the absence of water, a feature of the present invention is that it has the ability to tolerate small amounts of water, eg up to about 30% w/w based on the acetal reactant (II), and anhydrous conditions need not be used. This is a significant advantage since many hydrogenation catalysts such as eg Escat®10 contain water (moisture) . The present invention is further illustrated with reference to the following Examples. Examples 1-5 Unless otherwise stated, all parts and percentages are by weight and all temperatures in °C. In each of the Examples 1-5 below, the reactions were conducted in a 300 ml stirred autoclave equipped with a glass liner and a stirrer. The solvent, optionally water, and the acetal were weighed into the glass liner and mixed prior to removal of a small amount of sample for analysis by gas chromatography. The weighed amount of the catalyst composition was then added to the glass liner and placed inside the autoclave and sealed. The autoclave was purged three times with hydrogen and then filled with hydrogen to the specified pressure. The autoclave was heated to the specified temperature with stirring. Small samples were taken during the course of the reaction using a dip tube to monitor the extent of the reaction. A final sample was taken for analysis from the liquid obtained inside the reactor following cooling to room temperature and depressurization. Example 1 1.10 g of Escat®14 catalyst, 9.71 g of 3-ethoxypropionaldehyde diethyl acetal and 55.97 g of absolute ethanol are added to the glass liner and sealed in the autoclave. The initial hydrogen pressure is 1000 psig (6895 kPa) . The autoclave is then heated to a maximum temperature of 201°C. After 22 hours, the reaction temperature is raised to 216°C and the run is continued for 5 more hours. The product mixture obtained at the end of the run contains, in addition to ethanol, 88 mole % 1,3-diethoxypropane, 7 mole % 3- ethoxypropanol-1, 3 mole % 1-propanol and 2 mole % ethylpropyl ether. Example 2 1.0 g of a nominally 5% w/w palladium on silica catalyst, 10.38 g of 3-ethoxypropionaldehyde diethyl acetal and 56.80 g of absolute ethanol are added to the glass liner and sealed in the autoclave. The initial hydrogen pressure is 1000 psig (6895 kPa) . The autoclave is heated to a maximum temperature of 218°C. After 20 hours, the product mixture contains, in addition to ethanol, 84 mole % of 1,3-diethoxypropane, 15 mole % ethylpropyl ether and 1 mole % unreacted 3-ethoxypropionaldehyde diethyl acetal. Example 3 2.04 g of a 5% w/w palladium on carbon catalyst containing 55.3% w/w water is extracted with absolute ethanol to remove the water. The dried catalyst thus obtained, 9.75 g of 3- ethoxypropionaldehyde diethyl acetal and 56.72 g of absolute ethanol are added to the glass liner and sealed in the autoclave. The initial hydrogen pressure is 1000 psig (6895 kPa) . The autoclave is heated to a maximum temperature of 214°C. After 3.6 hours, the product mixture contains in addition to ethanol, 93 mole % 1,3- " diethoxypropane, 5 mole % of 3-ethoxypropanol-l and 2 mole % ethylpropyl ether. Example 4 2.08 g of Escat®10 catalyst, 9.97 g of 3-ethoxypropionaldehyde diethyl acetal and 55.85 g of absolute ethanol are added to the glass liner and sealed in the autoclave. The initial hydrogen pressure is 1000 psig (6895 kPa) . The autoclave is heated to a maximum temperature of 199°C. After one hour, the product mixture contains, in addition to ethanol, 71 mole % 1,3-diethoxy propane, 16 mole % 3- ethoxypropionaldehyde diethyl acetal and 13 mole % ethylpropyl ether. Example 5 1.025 g of Ni-3266 E catalyst defined above, 10.42 g of 3- ethoxypropionaldehyde diethyl acetal and 55.98 g of absolute ethanol are added to the glass liner and sealed in the autoclave. The initial hydrogen pressure is 910 psig (6275 kPa) . The autoclave is heated to a maximum temperature of 190°C. After 4.5 hours, the product mixture is found to contain, in addition to ethanol, 80 mole % 1,3-diethoxypropane, 20 mole % 3-ethoxypropanol-l. Preparation of 1, 1,3-triethoxypropane: A mixture of ethanol (6694g, 145.3 mol) and Amberlyst®15 (234 g) is stirred at 50°C. Acrolein (1726 g, 30.79 mol) is added, with stirring, over a period of 4 hours, and the mixture is stirred for a further 3 hours. The temperature is held at 50°C throughout. The mixture, containing ethanol (40.1% wt), acrolein (0.4% wt), 3-ethoxy- propanol (6.2% wt), acrolein diethyl acetal (0.3% wt), 1,1,3- triethoxypropane (45.1% wt) and water (4.8% wt) is filtered. The filtrate is vacuum distilled to give 1,1,3-triethoxyρropane (boiling point 98°C at 40mm Hg) identified by NMR analysis. Examples 6-16 A 500 ml zirconium autoclave equipped with stirrer, baffle cage and ballast vessel is charged with 300 ml of 1,1,3-triethoxypropane and a dry catalyst (which, if moist, is extracted with ethanol to remove any moisture present therein) under a nitrogen atmosphere. Having sealed the autoclave and commenced stirring, an initial charge of hydrogen is introduced such that a hydrogen atmosphere remained present during the period required to allow heating (generally 30 to 60 mins) but not such that the intended operating pressure (shown in the Table 1 below) is exceeded during this time. Once the stipulated operating temperature is attained, the ballast vessel is then employed to make up the hydrogen pressure to the desired value and maintain it at this value for the duration of the reaction. After allowing the autoclave to cool to ambient temperature, remaining hydrogen is vented and the product discharged and filtered prior to analysis. Table 1 below summarises the conditions and results of a sequence of Examples 6-16 which are all performed according to the general method outlined above. The following points should be noted. The catalyst charge is calculated on a dry weight per volume basis and the reaction time given is that time which elapsed with the reaction maintained at the stated conditions. Analysis is by gas chromatography calibrated against an internal standard. In Table 1, the following abbreviations have been used: EtOH - Ethanol TREP - 1,1,3-triethoxy propane DEP - 1,3-diethoxy propane EtOPr - ethyl propyl ether EP - ethoxypropanol TABLE 1 Ex |Pressure| Temp. |Catalyst cone. [Reaction |Product Composition, mass % |Conversion)Selectivity| No. I kPa I °C I w/v% ITime min |EtQH DEP TREP EtOPr EP [of TREP % | to DEP% | 6 9900 210 A 1.00 242 21.3 71.6 0.00 0.39 1.59 100 96.3 7 3400 150 A 0.67 378 25.2 68.0 4.23 0.47 2.88 95.7 95.7 8 4700 200 B 0.11 255 24.1 67.6 0.01 3.27 1.09 100 91.1 9 4800 160 B 0.06 306 24.3 70.7 0.02 0.36 1.19 100 95.3 10 2500 140 B 0.08 697 26.0 67.7 2.56 0.99 0.87 97.4 93.7 11 4800 160 B* 0.06 285 27.9 67.3 0.00 2.48 1.00 100 90.8 12 4800 160 C 0.13 635 24.5 69.4 4.29 0.15 1.33 95.7 97.8 13 4800 200 D 0.33 247 23.1 57.9 10.29 0.24 4.49 89.6 87.0 14 4800 160 E 0.17 625 26.1 66.0 1.14 2.17 1.40 98.8 90.0 15 4800 160 F 0.08 1080 20.1 49.5 25.87 0.99 0.71 73.9 90.2 16 6700 200 G 0.08 671 26.8 64.9 2.14 1.39 2.93 97.8 89.4 Notes: A = Escat®14, 5% Pd/Alumina, ex Engelhard B = Escat®10, 5% Pd/Carbon, ex Engelhard C = Escat®101, 5% Pd/Carbon, ex Engelhard D = 64% Ni/Silica-Alumina, ex Aldrich E = Product 4804, 10% Rh/Carbon, ex Engelhard F = Escat®23, 5% Pt/Carbon, ex Engelhard G = Escat®40, 5% Ru/Carbon, ex Engelhard * 50 mg of phosporic acid added (0.017% w/v)

Claims: Claims : 1. A process for making a 1,3-diether compound represented by the formula: RO.CH 2 .CH 2 .CH 2 .OR (I) wherein in formula (I) R is an alkyl group having 1 to 4 carbon atoms, the process comprising hydrogenating an acetal of the formula RO.CH 2 .CH 2 .CH(OR) 2 (II) wherein in formula (II) R has the same meaning as in formula (I) above, in the presence of a catalyst composition comprising at least one catalytic metal selected from the group consisting of Pd, Ni, Co, Pt, Rh and Ru and a support material, said support material being one or more materials selected from the group consisting of silica, alumina, silica-alumina, aluminosilicates and carbon. 2. A process accord-ing to Claim 1 wherein R in formula (II) is an ethyl group. 3. A process according to Claim 1 wherein said acetal is made by reacting acrolein with an alcohol and at least one acidic reagent for an effective period of time to form said acetal, said alcohol being represented by the formula R.OH wherein R has the same meaning as in formula (II) . 4. A process according to Claim 3 wherein in the reaction to make said acetal the molar ratio of acrolein to alcohol is about 1:1 to 1:20. 5. A process according to Claim 3 wherein in the reaction to make said acetal the reaction is conducted at a temperature in the range of about 0°C to about 120°C and a pressure in the range of about 0 kPa to 700 kPa . 6. A process according to Claim 1 wherein said acetal is converted to said diether at a hydrogen pressure of about 650 kPa to about 35,000 kPa. 7. A process according to Claim 1 wherein the mole ratio of said acetal to hydrogen is from about 1:1 to about 1:100. 8. A process according to Claim 1 wherein said support material is graphite or activated carbon. 9. A process according to Claim 1 wherein said catalytic metal is palladium and said support material is carbon. 10. A process according to Claim 1 wherein said acetal is converted to said diether at a temperature in the range from about 50°C to about 250°C. 11. A process for making 1,3-diethoxypropane comprising hydrogenating 3-ethoxypropionaldehyde diethyl acetal in the presence of a catalyst at a hydrogen pressure in the range of about 3,000 kPa to about 17,500 kPa and a temperature of about 150°C to about 210°C, said catalyst comprising a catalytic metal and a support material, said catalytic metal being Ni or Pd, said support material being selected from the group consisting of silica, alumina, silica- alumina, aluminosilicates and carbon. 12. A process for converting acrolein to 1,3-diethoxypropane comprising: contacting a mixture comprising ethanol and acrolein with at least one acidic reagent at a sufficient temperature and for an effective period of time to provide an intermediate product comprising 3-ethoxypropionaldehyde diethyl acetal; and hydrogenating said 3-ethoxypropionaldehyde diethyl acetal in the presence of a supported nickel or palladium hydrogenation catalyst at a sufficient temperature and for an effective period of time to form said 1,3-diethoxy propane, the support material for said catalyst being selected from the group consisting of silica, alumina, silica-alumina, aluminosilicates and carbon.

Inventors: BARTOSZEK-LOZA ROSEMARY, CIRJAK LARRY M, KLIEWER WAYNE R, BARTOSZEK-LOZA, ROSEMARY, CIRJAK, LARRY, M., KLIEWER, WAYNE, R.
Applicants: BARTOSZEK LOZA ROSEMARY, BP CHEM INT LTD, CIRJAK LARRY M, KLIEWER WAYNE R, BARTOSZEK-LOZA, ROSEMARY, BP CHEMICALS LIMITED, CIRJAK, LARRY, M., KLIEWER, WAYNE, R.
Application year: 1994
Main classification: C07C41
IPC codes: B01J23, C07B61, C07C41, C07C43